OSF/1 is based on the Mach 2.5 operating system from Carnegie Mellon University. Both are integrated or monolithic kernel systems that implement the majority of system functionality in the operating system kernel . Their kernels contain the core Mach technology and additional Unix functionality. OSF/1 has significantly upgraded the 4.3BSD portion of Mach 2.5 to implement advanced features and obtain compliance with standards. (en)